1. Field of the Invention
The present invention relates to an image processing apparatus and method for performing tone conversion and edge emphasis.
2. Description of the Background Art
A tone converting process and an edge emphasizing process are performed on an image captured by a digital camera and an image input to a computer by using predetermined hardware or software.
The tone converting process is a process of correcting the tone of an image in accordance with characteristics of a monitor, and the conversion characteristic is expressed by a γ (gamma) value. A general tone converting process is a converting process in which a γ value as the conversion characteristic is a constant value in a range from a shadow portion via a neutral portion to a highlight portion, and an output signal y to an input signal x is expressed as y=xγ.
The edge emphasizing process is performed by, for example, detecting and extracting a signal of a high frequency component from G (green) data of an image to be processed, and adding the extracted signal of the high frequency component to image signals of R, G, and B.
In an image processing apparatus such as a digital camera or the like, generally, first, the tone converting process is performed on input image data and, after that, the edge emphasizing process is carried out on the tone-converted image data.
As described above, the image processing apparatus such as a digital camera can output image data subjected to the tone converting process and the edge emphasizing process. In the above processing method, however, similar edge emphasis is performed in the range from the shadow portion to the highlight portion of an input image. Therefore, it cannot be said that an optimum edge emphasizing process is performed according to the input image.
For example, if an image captured by a digital camera is an image captured by macro shooting, it is preferable to enhance the edge emphasis as a whole. If the image is an image of night view, a dark portion is large, so that it is necessary to remove noise in a low luminance portion.
In Japanese Unexamined Patent Application No. 2000-115539, density determination is made, and the degree of emphasizing an edge is changed according to density. However, since the density determination is made, there is a problem such that processing time is long.
In Japanese Unexamined Patent Application No. 11-32236, luminance determination is not performed but a backlight scene is determined. In the case of a backlight scene, the degree of edge emphasis is suppressed. However, since the degree of edge emphasis is unconditionally adjusted irrespective of the luminance, there is a problem such that sharpness of a whole image deteriorates.